Emission Spectrochemical Analysis of Metals Using a Nitrogen Laser

Comparative studies of the possibilities of using pulsed nitrogen and Nd:YAG lasers for emission spectrochemical analysis of copper-zinc alloys have been made. The nitrogen laser developed on the basis of the commercial excimer laser provided an energy of radiation pulses of 5 mJ with an error of less than 0.8% at a repetition frequency of 100 Hz. The high stability and the high pulse repetition frequency of the nitrogen laser were attained due to the additional high-speed fan inside the laser chamber, which provided agitation and circulation of the gas mixture. It has been shown by experiment that the spectral emission of the plasma formed by means of the nitrogen laser is characterized by intensity fluctuations with a root-mean-square deviation of 1.4%, whereas in the case of using an Nd:YAG laser it was 14.3%. The advantages of the nitrogen laser that are due to the increased signal-to-background ratio and the suppression of the selective evaporation effect have been revealed.     

由半导体激光器端面输出谱确定自发辐射谱

利用射线法和平均载流子分布近似，从理论上预言了用阈值以下半导体激光器的端面输出谱来确定自发辐射谱的可能性。在此基础上，通过实验测得的阈值以下半导体激光器的端面输出谱确定了自发辐射谱，并且对自发辐射谱和增益谱进行了比较和分析。     

基于脉冲CO2激光锡等离子体光刻光源的极紫外辐射光谱特性研究

研究了不同条件下脉冲放电CO₂激光烧蚀平板锡靶产生的等离子体极紫外辐射特性, 设计并建立了一套掠入射极紫外平焦场光栅光谱仪, 结合X射线CCD探测了光源在6.5～16.8 nm波段的时间积分辐射光谱,得到了极紫外光谱随激光脉宽, 入射脉冲能量及背景气压的变化规律。实验结果发现：入射激光脉冲能量在30～600 mJ变化时,极紫外辐射光谱的强度随辐照激光脉冲能量的增加而增加, 但并不是线性关系, 具有饱和效应, 且产生极紫外辐射的脉冲能量阈值约为30 mJ,当激光脉冲能量为425 mJ时具有最高的转换效率,此时中心波长13.5 nm处2%带宽内的转换效率约为1.2%。激光脉冲半高全宽在50～120 ns范围内变化时, 极紫外辐射光谱的峰值位置均位于13.5 nm,光谱形状几乎没有什么变化, 但是脉宽从120 ns变到52 ns后,由于激光功率密度的提高,极紫外辐射强度也随之增强了约1.6倍。极紫外光谱的强度随背景气压的增大而迅速下降, 当腔内空气气压为200 Pa时, 极紫外辐射光子几乎被全部吸收,而当缓冲氦气气压为7×104 Pa时,仍能够探测到微弱的极紫外辐射信号,计算表明100 Pa的空气对13.5 nm极紫外光的吸收系数为3.0 m-1,而100 Pa的He气的吸收系数为0.96 m-1。     

火焰发射光谱对K元素激光诱导击穿光谱测量的影响

在煤和生物质燃烧过程中,燃料中的碱金属元素会发生气态释放,并在随烟气降温的过程中凝结,产生热力设备结渣、腐蚀、积灰等问题,影响设备的安全运行。激光诱导击穿光谱(LIBS)技术是测量煤/生物质火焰中碱金属元素分布的有效手段。建立了一套火焰场内K元素的LIBS测量系统,分别测量了不同ICCD门宽时间条件下火焰场内K元素的火焰发射光谱(FES)信号和LIBS信号,并计算、比较了二者的信号强度随测量系统ICCD门宽时间变化的规律。实验结果表明,相同ICCD门宽时间条件下,火焰场内K元素LIBS信号强度显著高于FES信号强度。随着ICCD门宽时间的增加,二者的信号强度均逐步增加,但是二者的增速变化规律并不相同:K元素LIBS信号强度的增加速度呈现出先快后慢的变化规律;K元素FES信号强度则呈现出线性增加的规律。同时,相同ICCD门宽时间条件下,K元素LIBS信号强度与FES信号强度的比值在ICCD门宽时间为0~8μs的范围内迅速升高至约4;之后,随着ICCD门宽时间的增加,该比值缓慢下降并逐步趋近于1。通过分析火焰场内K元素FES对LIBS测量影响的原理,提出了合理选取LIBS测量系统ICCD门宽时间,使得K元素LIBS信号强度与FES信号强度的比值最大化,从而降低K元素FES对LIBS测量影响,优化了提高火焰场内K元素LIBS信号测量准确度的方法。     

Dynamics of the Emission of Light by C2 and C3 Molecules in a Laser Plasma Produced by Two-Pulse Irradiation of the Target

The laser plasma produced by irradiation of a graphite target simultaneously by the first and second harmonics of two Nd³⁺:YAG lasers has been studied by emission spectroscopy methods. The delay between radiation pulses () varied from 0 to 700 sec. It is established that in the absence of a delay between pulses ( = 0) the increase in the intensity of plasma emission at the wavelengths corresponding to the radiative transitions of the C₂ and C₃ molecules is of nonradiative character. The plasma produced by laser radiation at the wavelength = 1064 nm exerts its influence on the radiation spectrum of the plasma produced by laser radiation at the wavelength = 532 nm, if the magnitude of the delay between laser pulses does not exceed 30 sec. The most probable reason for this character of influence of the prepulse on the laser plasma radiation spectrum is sublimation of soot particles caused by laser radiation at = 532 nm.     

Wavelength Shift Investigation of Optical Emission from Nanosecond Pulsed Laser Ablated Metal Al

The wavelength shift of optical emission from pulsed laser ablation of metal Al in 1atm air has been investigated by using the time-resolved optical emission spectroscopy (OES). The wavelength shift of OES has a second order exponential decay with time and was also found to be significantly influenced by the laser ablated pulse energy. By taking account of the shielding effect of free electrons inside of the plasma plume, the relation between the electron density and wavelength shift has been discussed.     

The Gravitational Field of a Circulating Light Beam

Exact solutions of the Einstein field equations are found for the exterior and interior gravitational field of an infinitely long circulating cylinder of light. The exterior metric is shown to contain closed timelike lines.     

发射光谱法研究纳秒激光烧蚀硅等离子体特性

利用调Q Nd3+∶YAG激光器三倍频355 nm激光脉冲烧蚀空气环境的硅样品,观测不同脉冲激光能量下产生的等离子体在380～420 nm范围内的时间-空间分辨等离子体发射光谱,观测到在等离子体羽膨胀初期存在N+发射光谱。在局域热力学平衡近似条件下,根据时间-空间分辨等离子体发射光谱计算得到等离子羽体电子温度和电子密度随时间延时存在二次指数衰减变化,等离子体羽体电子温度和电子密度的空间分布近似呈Lorentz分布,发现在确定激光脉冲能量下电子密度空间分布最大值偏离光谱强度最大空间位置并对产生原因进行分析,探讨了等离子体羽参数与激光脉冲能量的关系。     

抽运光波前畸变对拍瓦激光器前端OPA光束质量的影响

数值模拟了拍瓦激光器前端非共线光参变放大(OPA)过程中存在波前畸变的抽运光对信号光光束质量的影响.结果表明,当抽运光光束波前存在严重畸变时,衍射效应和走离效应通过不同的物理机制导致了信号光光束质量的急剧下降.在导致信号光光束质量下降的过程中,走离效应在OPA未饱和放大时起着主导作用,当OPA工作在过饱和状态时,过饱和导致的信号光近场空间分布中心凹陷成为光束质量下降的主要因素.     

脉冲激光烧蚀碲镉汞材料的等离子体发射谱

脉冲激光辐照处于不同背景气压下的Hg0.8Cd0.2Te材料表面,用时间和空间分辨诊断技术探测了激光照射后产生的等离子体发射谱,根据所获得的飞行时间谱测量了等离子体中粒子的出射速度,结果表明粒子速度随着出射距离的增加迅速减小,且背景气压对出射速度有很大的影响,而激光能量对粒子速度的影响不大。另外根据谱线的展宽计算了等离子体中的电子密度,结果表明,电子密度在激光辐照样品后的短时间内迅速减小,且电子密度最大的位置不是出现在靶的表面而是在距表面一定距离处。     

压缩真空中的三能级原子的自发辐射强场高次谐波时间特性的理论分析

对压缩真空与V型三能级原子的相互作用作了理论分析, 探讨了量子干涉效应对压缩真空中原子自发辐射的影响。当原子的上能级简并时强的量子干涉效应影响原子的定态和定态出射光谱, 使它们对原子的初态敏感。这种情况下, 压缩使谱线趋于关于压缩真空中心频率对称, 量子干涉使谱线趋于不对称。通过用单电子近似求解含时薛定谔方程, 用加窗傅里叶分析的方法, 分析了单原子产生的高次谐波的时间特性。理论分析表明, 基态粒子数消耗对不同级次谐波辐射的影响程度不一样; 谐波辐射随着入射激光场强度的增加会出现饱和; 随着谐波级次的增加, 谐波辐射越来越趋向于集中在更短的时间间隔内, 相应的线宽也随着谐波级次的增加而增加。     

Physical Analysis of a Possibility to Reach the 1.30-μm Emission from the GaAs-Based VCSELs with the InGaAs/GaAs Quantum-Well Active Regions and the Intentionally Detuned Optical Cavities

Physical aspects of an operation of the GaAs-based InGaAs/GaAs quantum-well (QW) VCSELs with the intentionally detuned optical cavities have been considered in the present paper using the comprehensive three-dimensional self-consistent optical–electrical–thermal-gain simulation. In GaAs-based structures, very good DBR resonator mirrors and a very efficient methods to confine radially both the current spreading and the electromagnetic field with the aid of oxide apertures may be applied. It has been found using the above simulation that even currently available immature technology enables manufacturing the above devices emitting radiation of wavelengths over 1.20 μm. In particular, while the room-temperature 1.30-μm lasing emission is still beyond possibilities of the InGaAs/GaAs QW VCSELs, these structures may offer analogous 1.25-μm emission, especially for the high-power and/or high-temperature operation.     

Intermittent Emission of Particles from a Bose-Einstein Condensate in a 1D Lattice

Particle emission from a Bose-Einstein condensate with periodically modulated interactions is investigated in a 1D lattice. Within perturbative analysis, which leads to instabilities for discrete modes, the main regimes are obtained where the system can emit a large particle jet, and the distinctly intermittent rather than continuous emission is found. The time evolution of the trapped particles exhibits a stair-like decay, and a larger drive induces a more significant intermittency. This study further sheds light on the dynamics of the stimulating process, and demonstrates that instead of a real suspension, the intermittency represents a build-up stage of the system. The theoretical framework might be generalized to the explorations on multiple-site systems with analogous configurations and couplings, and offer new insights into other fundamental nonequilibrium problems.     

Talbot Images of an Array Source with Correlated Phase Fluctuation Using the Propagation Law of a Gaussian Beam

Talbot images of a two-dimensional array source such as a surface-emitting array laser are investigated with the help of the propagation law of a Gaussian beam. The effect of the phase fluctuation existing between the elements of the source on the formation of Talbot images is revealed by computer simulation. In the study, the correlation extent of the phase fluctuation is taken into consideration together with its magnitude (standard deviation), and Talbot images of good quality are found to be formed when the correlation extent is larger than the extent of the diffraction of a Gaussian beam in the observation plane. It is further shown that the contrast of Talbot images is governed, in a statistical sense, not by the magnitude of the phase itself but by the phase-fluctuation slope in the array source.     

环镜对激光束变换的理论分析与实验

介绍一种新型的光学元件，它可把一束激光变换成一个两维的激光平面。本文用多光束干涉的原理解释了光平面形成的原理，同时对应用前景及实用情况也作了一些估计     

Structure Optimisation of a Possible 1.5-μm GaAs-based Vertical-cavity Surface-emitting Laser Diode with the GaInNAsSb/GaNAs Quantum-well Active Region

Structure optimisation of the GaAs-based GaInNAsSb/GaNAs quantum-well (QW) vertical-cavity surface-emitting diode lasers (VCSELs) has been carried out using the comprehensive three-dimensional self-consistent physical model of their room-temperature (RT) continuous-wave (CW) threshold operation. The model has been applied to investigate a possibility to use these devices as carrier-wave lasing sources in the third-generation optical-fibre communication. In this simulation, all physical (optical, electrical, thermal and gain) phenomena crucial for a laser operation including all important interactions between them are taken into consideration. As expected, the 1.5λ-cavity VCSEL has been found to demonstrate the lowest RT CW threshold. However, for many VCSEL applications, the analogous VCSEL equipped with a longer 3λ-cavity should be recommended because it exhibits only slightly higher threshold but manifest much better mode selectivity – the desired single-fundamental-mode operation has been preserved in these devices up to at least 380 K. The Auger recombination has been found to be decidedly the main reason of the threshold current increase at higher temperatures. A proper initial red detuning of the resonator wavelength with respect to the gain spectrum may drastically decrease CW lasing thresholds, especially at higher temperatures.     

Influence of the Gaseous Medium on the Spectral Emission of Microplasma Obtained in Evaporating a Sample with the Aid of Laser Radiation

An investigation is made of the influence of air, oxigen, argon, and neon-helium atmosphere on the spatial distribution of the glow of microplasma, obtained in treating a brass sample with laser radiation and excited with the aid of a subsidiary synchronous discharge. The plasma's luminous zone, from which the spectral lines are recorded, extends when the inductance of the discharge circuit is lower and when an inert gaseous medium is used. The maxima of the intensities of the spectral lines with higher excitation energies appear at greater heights from the sample's surface.     

Simultaneous Laser-Induced Fluorescence Imaging of Unburnt and Reacting Areas in Combustion Fields Using a KrF Excimer Laser

Simultaneous two-dimensional imaging of an unburnt area and a reacting area was performed using laser-induced fluorescence. Acetone was added to fuel as a tracer, and OH radical was used as a marker of the reacting area. A narrow band tunable KrF excimer laser (248 nm) was employed to excite acetone and OH simultaneously. Two intensified CCD cameras with different wavelength filters were used to detect these two kinds of species respectively. Detecting 294-314 nm (A-X (3, 2), etc.) for OH and 335-410 nm for acetone, we obtained images of each species without interference of a signal from the other. The method was also successfully applied to flames in a pressurized combustion chamber under the pressure of 0.5 MPa.     

Generation of THz Radiation from Laser Beam Filamentation in a Magnetized Plasma

The terahertz (THz) frequency radiation production as a result of nonlinear interaction of high intense laser beam with low density ripple in a magnetized plasma has been studied. If the appropriate phase matching conditions are satisfied and the frequency of the ripple is appropriate then this difference frequency can be brought in the THz range. Self focusing (filamentation) of a circularly polarized beam propagating along the direction of static magnetic field in plasma is first investigated within extended‐paraxial ray approximation. The beam gets focused when the initial power of the laser beam is greater than its critical power. Resulting localized beam couples with the pre‐existing density ripple to produce a nonlinear current driving the THz radiation. By changing the strength of the magnetic field, one can enhance or suppress the THz emission. The expressions for the laser beam width parameter, the electric field vector of the THz wave have been obtained. For typical laser beam and plasma parameters with the incident laser intensity ≈ 10¹⁴ W/cm², laser beam radius (r₀) = 50 μm, laser frequency (ω₀) = 1.8848 × 10¹⁴rad/s, electron plasma (low density rippled) wave frequency (ω₀) = 1.2848 × 10¹⁴ rad/s, plasma density (n₀) = 5.025 × 10¹⁷cm^–3, normalized ripple density amplitude (μ)=0.1, the produced THz emission can be at the level of Giga watt (GW) in power (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)